In the above displays, when light emitted mainly from the interior of the display goes straight without diffusion on the surface of the display, the surface of the display, when viewed with the naked eye, is in the glare of the light. In order to prevent this phenomenon, an antiglare film for diffusing the light emitted from the interior of the display to some extent is provided on the surface of the display.
For example, Japanese Patent Laid-Open Publication Nos. 18706/1994 and 20103/1998 disclose antiglare films formed by coating a resin containing a filler, such as silicon dioxide (silica), onto the surface of a transparent substrate film.
These antiglare films are classified into a type wherein concaves and convexes are formed on the surface of the antiglare layer by coagulation of particles, such as coagulative silica, a type wherein organic fillers having a particle diameter larger than the coating thickness are added to a resin to form concaves and convexes on the surface of the layer, and a type wherein a film having thereon concaves and convexes is laminated on a layer to transfer the concaves and convexes onto the layer.
In all the types of the above conventional antiglare films, light diffusing/antiglare action is created by the surface shape of the antiglare layer, and increasing the size of concaves and convexes is necessary for enhancing antiglare properties. Increasing the size of concaves and convexes, however, increases the haze of the coating and in its turn disadvantageously lowers the transmissive visibility.
A light-diffusive film similar to the above antiglare films is disclosed, for example, for a reflection type liquid crystal display device (Journal of the Illuminating Engineering Institute of Japan MD-96-48, 277-282 (1996)). In this light-diffusive film, fine particles are dispersed within the layer to attain a light diffusion effect.
In order to attain satisfactory light diffusion effect by the contemplated internal scattering effect, the diameter of the fine particles should be increased. This poses a problem in that the sharpness of images is very low although the haze is high.
When a film for attaining light diffusion effect by the internal scattering effect, such as the light-diffusive film, is provided on the surface of a display for antiglare purposes, the reflection of external light on the surface of the display cannot be prevented because the surface of the film is substantially flat. That is, the film does not disadvantageously have the so-called "external light reflection preventive properties."
In addition, in the conventional antiglare films described above, shining called "scintillation" occurs on the film surface, disadvantageously leading to deteriorated visibility of the display screen.
For the antiglare films, haze is one of the evaluation criteria. Lowering the haze of the surface increases shining called scintillation. When the haze is increased in order to eliminate this problem, the whole image becomes whitish and the black density is lowered. This unfavorably results in lowered contrast. On the other hand, lowering the haze for removing the whitening effect disadvantageously increases the so-called "external light reflection" and "shining."
With a view to solving the above problems, the present inventors have developed an antiglare film which, without sacrificing the diffusing and antiglare properties, can improve the sharpness of transmitted images, can lower scintillation, and has external light reflection preventive properties. An application relating to this antiglare film has been filed as Japanese Patent Laid-Open No. 126494/1998.
In order to realize the above properties, the haze should be regulated by the internal scattering effect. The internal scattering effect can be regulated by regulating the mixing ratio of the light-transparent fine particles and the light-transparent resin, the difference in refractive index between the light-transparent fine particles and the light-transparent resin, the particle diameter of the light-transparent fine particles, and the thickness on a dry basis of the antiglare layer.
The regulation of the mixing ratio, the particle diameter, and the coating thickness, however, affect the surface shape. Therefore, the haze cannot be solely regulated while maintaining a certain level of sharpness of transmitted images, that is, external light reflection preventive properties.
The internal scattering effect can also be regulated by the refractive index of the light-transparent fine particles. The regulation of the refractive index, however, disadvantageously causes a limitation on the regulation of the haze.